1. Field of the Invention
The present invention relates to a node device for reserving an optical path in an optical communication network using wavelength division multiplexing by a distributed control method, an optical communication network comprising this node device, an optical path reserve method, and a computer-readable medium comprising a program thereof.
2. Description of Related Art
Communication demands are rapidly increasing lately due to the spread of the Internet and other reasons. To support these demands, high-speed and large capacity optical communication networks using optical fibers are being organized. WDM (Wavelength Division Multiplexing) is receiving attention as a technology used for these optical communication networks. WDM is a technology to multiplex optical signals of which carriers have different wavelengths. By using WDM, a plurality of carriers can be propagated through one optical transmission line in parallel. Therefore large capacity optical communication networks can be constructed at low cost.
An optical communication network using WDM comprises a plurality of node devices and optical transmission lines. Each node device has a router. An optical transmission line is an optical fiber, and connects the node devices. In an optical communication network using WDM, each node device has a means to implement OADM (Optical Add Drop Multiplexer) and OXC (Optical Cross-Connect) functions. OADM is a function to multiplex a carrier having another wavelength into optical signal which has been wavelength-multiplexed by WDM, or to demultiplex a carrier having a specific wavelength from optical signal which has been wavelength-multiplexed by WDM. OXC is a function to switch the propagation paths of a carrier which has been wavelength-multiplexed by WDM in wavelength units. By using these functions, an optical paths layout comprised of a plurality of optical paths, that is, a logical topology, can be constructed on an optical communication network comprised of node devices and optical transmission lines, that is a physical topology.
A method for recovering communication status when a communication is interrupted by failure or congestions in an optical communication network using WDM has been provided. According to this method, an optical path in which communication is being interrupted is avoided by dynamically changing the optical path layout. To change the optical path layout, a failure or congestion block is detoured, or the node device where congestion occurred is cut-through. “Cut-through” here means allowing optical signals to pass through the node device using only OADM or OXC, without using the routing function of this node device. By setting a cut-through path in the node device where congestion occurred so as not to use the routing function, the processing load of this node device can be decreased.
A method for setting a cut-through path in an optical communication network is either a centralized control method (e.g. Japanese Patent Application Laid-Open No. 2002-261791) or a distributed control method (e.g. Japanese Patent Application Laid-Open No. 2003-235060).
In the case of the central control method disclosed in Japanese Patent Application Laid-open NO. 2002-261791, a centralized control device receives network resource information from all the node devices belonging to the optical communication network, reserves optical paths using this network resource information, then sends control signals to each node device to set optical paths. Therefore the processing load in the centralized control device increases if the number of node devices increases and the network scale is expanded. An increase in the processing load in a centralized control device may increase the processing time required until path setting completes.
In the case of the distributed control method disclosed in Japanese Patent Application Laid-Open No. 2003-235060, on the other hand, available wavelengths are reserved by transmitting/receiving wavelength reserve signals between node devices on a predetermined physical path, and an optical path is set using this wavelength. According to this distributed control method, an increase of processing time due to an expansion of the network scale, which is the problem of the above mentioned centralized control method, can be suppressed.
In the case of the distributed control method disclosed in Japanese Patent Application Laid-Open No. 2003-235060, however a blocking, which is a phenomena in which a wavelength cannot be reserved if there is no available wavelength to reserve on this predetermined physical path, occurs. If blocking occurs, a wavelength is reserved after other physical paths are determined, so the time required until path setting completes may become long.
After devoted study, the inventor related to this application discovered that optical paths can be efficiently reserved if the selection of paths and selection of wavelengths on the selected paths are performed simultaneously in path setting by the distributed control method.
With the foregoing in view, it is a first object of the present invention to provide a node device which can suppress the increase of processing time due to the expansion of the network scale by reserving optical paths by a distributed control method in the optical communication network using WDM, and can decrease the time until reserving optical paths completes by deceasing the probability of the occurrence of blocking. It is a second object of the present invention to provide an optical communication network comprising this node device. It is a third object of the present invention to provide an optical path reserve method which can suppress the increase of processing time due to expansion of the network scale by reserving optical paths by a distributed control method in the optical communication network using WDM, and can decrease the time until reserving optical paths completes by decreasing the probability of the occurrence of blocking. It is a fourth object of the present invention to provide a program which executes this optical path reserve method.